Ordinarily, as fuels in combustion appliances, such as lighters for smoker's requisites, other types of lighters, torches, and illumination devices, alcohol fuels, such as ethyl alcohol, petroleum benzine types of benzine fuels, or liquefied gas fuels, such as butane gas or propane gas, have heretofore been utilized.
The performances, the levels of convenience of handling, and the design structures of the combustion appliances vary in accordance with the kinds of the fuels used, and the fuels have their own features. For example, in cases where the liquefied gas fuels are used as the liquid fuels, since the liquefied gas fuels have a high gas pressure at temperatures falling within the range, in which the combustion appliance is used, the vessel for storing the fuels must have a pressure-resistant structure. Also, the flame length varies in accordance with variations in gas pressure. In particular, the liquefied gas fuels have the characteristics such that their gas pressures markedly vary logarithmically with respect to temperatures, and therefore the problems occur in that the flame length changes markedly, depending upon temperatures. In order for the change in flame length to be reduced, a special design countermeasure for carrying out temperature compensation for a fuel feeding mechanism of the combustion appliance must be taken. Therefore, the structure cannot be kept simple, and the cost cannot be kept low.
As for the liquid fuels, such as the alcohol fuels, they are liquids at normal temperatures and have comparatively low vapor pressures. Therefore, the fuel storing section need not have a pressure-resistant structure. Accordingly, the structure of the combustion appliance can be kept simple, and the cost can be kept comparatively low. In the combustion appliances for the liquid fuels, ordinarily, as means for feeding the liquid fuel from the fuel storing section to the burning section, a combustion wick, which sucks up the liquid fuel with the capillarity through open pores or through minute spaces formed between thin fibers in a fiber bundle and by the utilization of the surface tension of liquid fuel and allows the liquid fuel to burn at a top end portion of the wick, has heretofore been used.
Specifically, in the combustion wick, the liquid fuel is sucked up by the utilization of a string-like wick formed by twisting fibers, a bundle of glass fibers, a wick formed by bundling glass fibers with cotton threads and interweaving thin metal wires for preventing the bundle from becoming loose, or the like. The lower end portion of the combustion wick has the functions for sucking up the liquid fuel, and the sucked-up fuel is burned at the top end portion of the wick.
However, with the combustion wick, in which the fuel sucking portion and the burning portion are made from the same material and formed as an integral body, both of the requirement for the performance for sucking up the liquid fuel from the fuel storing section and the requirement for the combustion performance cannot be satisfied sufficiently.
For example, a combustion wick, in which the sucking portion is made from the same material as the heat-resistant material of the burning portion and the two portions are formed as an integral body, may be used. Also, the lower portion of the combustion wick may be inserted into the fuel storing section having been injected with the liquid fuel, and the liquid fuel may be lighted and burned at the upper portion of the combustion wick. In such cases, when the amount of the fuel in the fuel storing section becomes small due to the use of the fuel for the burning at the burning portion and the distance, over which the fuel is to be sucked up from the fuel storing section to the burning portion, becomes long, the rate of the sucking of the fuel through the sucking portion becomes low, and the rate of fuel feeding to the burning portion becomes low. As a result, the flame length becomes short. However, if the thickness of the combustion wick is set to be large such that the sucking performance of the sucking portion may be enhanced, the flame length will become long, or the flame thickness will become large. Thus the combustion wick has the problems in that a combustion flame having characteristics suitable for the application of the combustion appliance cannot be obtained.
In cases where the combustion wick is made from a material, which has good sucking performance but has a low heat resistance, the problems occur in that adverse effects of heat during the combustion occur quickly on the characteristics of the combustion wick. As a result, the flame length varies, and good durability cannot be obtained. Conversely, with a combustion wick which has good combustion characteristics but has insufficient sucking performance as described above, a stable flame length cannot be obtained.
Further, in the cases of lighters for smoker's requisites, and the like, it is often desired that the combustion flame can be rendered small or can be extinguished after the combustion has been continued for a predetermined length of time. In cases where a combustion wick having such characteristics is to be constituted, it is difficult for the combustion wick, in which the sucking portion and the burning portion are made from the same material and formed as an integral body, to satisfy both of the requirement for the fuel sucking characteristics and the requirement for the combustion characteristics.
In view of the above circumstances, the object of the present invention is to provide a combustion wick in a combustion appliance for a liquid fuel, which combustion wick has combustion characteristics appropriate for the application of the combustion appliance.